The present invention relates generally to radioactive sources used in the treatment of cancerous tissue. More particularly, the invention resides in apparatus, and methods for producing apparatus, incorporating a high dose radioactive source to be delivered into the body of a cancer patient for relatively short term but repeated exposure of a malignant tumor to localized in vivo radiation from within. The delivery may be through a catheter which terminates at or beyond the tumor site.
The type of radiation treatment of malignant tumors most often performed involves directing a beam of radiation from a point external to the patient's body onto the area of the body in which the tumor is located, for the purpose of shrinking and ultimately destroying the tumor. Such treatment is not particularly selective except in a somewhat gross sense, and therefore exposes healthy tissue to the high dosage of radiation in the beam and consequent potential injury. Another technique for radiation treatment, known as brachytherapy, attacks tumors from within the body. The brachytherapy method generally employs a highly radioactive source integral with a guidewire (the entire unit being referred to herein as a source wire) which is typically delivered via a catheter (although it may be delivered through a natural cavity, duct or vessel of the body) directly to the tumor site for localized irradiation. The latter technique is less likely to expose healthy tissue to injury than if external beam radiation were used. One or more catheters, for example, are implanted in the patient's body to provide a path from an external point to and through the tumor site, so that the interior of the tumor mass is accessible via the catheter(s). The radioactive source, with the typical dose available in the prior art being up to a range of eight or nine curies, is then mechanically delivered on the retractable guidewire through the catheter for localized irradiation of the tumor for a very short period of time, usually in the range of only seconds up to a few minutes per treatment.
The high dose source is secured to the tip of the guidewire, the other end of which is attached to a controllable apparatus known as a remote afterloader, for advancement or retraction. Advancement of the source wire through the catheter to the proper location for treatment of the tumor is achieved by calibration according to the measured distance traveled by a previously advanced and retracted dummy wire having an opaque tip marker for fluoroscopic observation. The source wire is left in the selected position for a predetermined time interval (programmed into the afterloader) deemed necessary to provide the desired treatment, and is then automatically retracted and returned to a shielded storage area within the afterloader.
The treatment regime is usually repeated at regular short intervals over a period of many days, weeks or months until the tumor has been completely eliminated or at least shrunk to the maximum practicable extent. Among the advantages of this type of radiation therapy are exposure of the tumor to fractionated treatment doses of localized radiation so that each individual treatment need only be of extremely short duration to provide the desired effect while reducing the extent of patient discomfort, and to provide more rapid shrinking of the tumor while avoiding prolonged exposure of healthy tissue to radiation.
Because this type of therapy is more applicable to inoperable malignancies deep within the body, the site of the tumor(s) is usually difficult to reach as the source wire is guided through the path provided by the implanted catheter. It is often the case that this path is long, narrow and tortuous with numerous sharp turns. It is essential, therefore, that the source wire should be extremely thin and flexible. This means it is necessary that the radioactive source, the core, must be sufficiently small to traverse the path to and from the tumor, and yet, be capable of delivering a radiation dosage at least as high and, desirably, even higher than that available in the highest dosage prior art devices, namely, up to ten curies.
One material frequently used for hot (radioactive) cores capable of delivering high dosage radiation to the tumor site by means of a remote afterloader is substantially pure iridium, which can be irradiated to a relatively high level of radioactivity as Ir-192, in a relatively small size. Ir-192 has been produced by prior art techniques in a nuclear reactor with dosages of up to 10 curies in a diameter small enough to allow a source wire diameter of about 1.1 millimeters (mm). Other conventional source materials include cobalt, cesium, palladium, gold, and iodine.
The foremost technique employed in the prior art for fabricating source wires starts with building the radioactive core by first stacking a plurality of small irradiated disks and then pinning them together through their common central hole. Unfortunately, this approach has not been successful in producing a sufficiently high dose radioactive core in a package size suitable for fabricating a source wire thin enough to traverse the smallest catheters of interest for interstitial and/or intraluminal brachytherapy. Moreover, the disks can be difficult to handle, and present a serious contamination problem if, during assembly or upon breakage of the source wire, they should spill out of their pinned or otherwise contained configuration.
It is a principal object of the present invention to provide a new and improved radioactive source or core for in vivo localized radioactive treatment of malignant tumors, and which can be produced with radioactivity levels of at least 10 curies in a smaller package than has heretofore been attainable.
It is another important object of the present invention to provide an improved design and method of fabrication for a high dose radioactive source for use in interstitial, intraluminal and/or intracavitary brachytherapy.